No, astigmatism shows as an out of focus star which is oval. When you rotate the mirror in its cell, the axis of rotation will change with it.

Someone ask you to mask off the outer edge (of the tube, or the mirror). That's a good suggestion. *If* the spikes were evenly distributed all the way around, it would be a fairly simple diagnosis, which you confirm by masking the edge, and seeing if the spikes go away. But that's the way modern machines would create TDE (turned down edge). But you have an f/8.3 which is an unusual focal length for mass produced Newts and suggests that your mirror was made by an amateur telescope maker (atm). A hand ground mirror by an atm who was just learning might have something odd like TDE in some parts of the mirrors and not others. The bigger your mirror the more likely you will have TDE.

It is also possible that you have TDE *and* a mispositioned secondary or primary misalignment.

Bad TDE shows itself as long tendrils that come out of a star that is in focus. There will be the classic four spikes from the secondary and then the tendrils will be long and thin and come out way past the vane spikes. But where TDE is less severe you get shorter spikes, and what you have in your pic is not particularly bad if that is all there is. Still, if they go away when you mask the outer edge of the mirror, that is a hint.

The bad news is that I had a mirror which showed asymmetric spiking like that, it was almost as if the spike was a stick and the star a popsicle. This effect showed even on planets such as Jupiter. The mirror in question was badly deformed by incomplete annealing and now serves as a doorstop. A foucault test might show a grand canyon type valley in the mirror. In my case the mirror was so bad you could see three ghost images of Jupiter in addtion to Jupiter when in focus. There is a currently active thread about replacing a GSO mirror that has the pics. I'll try to find the link. We cannot rule out (yet) that you have a similar defect, but perhaps not as severe. In any event even a less severe fracture than what I had would prove fatal to the mirror's prospects.

No, astigmatism shows as an out of focus star which is oval. When you rotate the mirror in its cell, the axis of rotation will change with it.

Someone ask you to mask off the outer edge (of the tube, or the mirror). That's a good suggestion. *If* the spikes were evenly distributed all the way around, it would be a fairly simple diagnosis, which you confirm by masking the edge, and seeing if the spikes go away. But that's the way modern machines would create TDE (turned down edge). But you have an f/8.3 which is an unusual focal length for mass produced Newts and suggests that your mirror was made by an amateur telescope maker (atm). A hand ground mirror by an atm who was just learning might have something odd like TDE in some parts of the mirrors and not others. The bigger your mirror the more likely you will have TDE.

It is also possible that you have TDE *and* a mispositioned secondary or primary misalignment.

Bad TDE shows itself as long tendrils that come out of a star that is in focus. There will be the classic four spikes from the secondary and then the tendrils will be long and thin and come out way past the vane spikes. But where TDE is less severe you get shorter spikes, and what you have in your pic is not particularly bad if that is all there is. Still, if they go away when you mask the outer edge of the mirror, that is a hint.

The bad news is that I had a mirror which showed asymmetric spiking like that, it was almost as if the spike was a stick and the star a popsicle. This effect showed even on planets such as Jupiter. The mirror in question was badly deformed by incomplete annealing and now serves as a doorstop. A foucault test might show a grand canyon type valley in the mirror. In my case the mirror was so bad you could see three ghost images of Jupiter in addtion to Jupiter when in focus. There is a currently active thread about replacing a GSO mirror that has the pics. I'll try to find the link. We cannot rule out (yet) that you have a similar defect, but perhaps not as severe. In any event even a less severe fracture than what I had would prove fatal to the mirror's prospects.

p.s. in addition to masking the mirror another test--for the kind of fracture in the link--is to rotate the mirror in the cell and see if the defect rotates with it. A defect in your *alignment* ought not to rotate with the mirror.

Just a quick update, I am actually testing tonight and I'll try to do a few of the suggestions here. I'll mask the outer edge to see if I can block whatever is causing the spikes. Also I will, if I can, try to rotate the mirror.

One thing I have done in the interim is I followed the procedure in another thread for using a webcam, properly centered in the focuser, to align the optics. I found a few things that were not right. Mainly the secondary mirror was not aligned correctly. I have been testing another OTA but I'll have time tonight for this one and I'll see what I can find out.